1. Field of the Invention
The present invention relates to a magnet plate for a linear motor for preventing misalignment of magnets.
2. Description of the Related Art
A magnet plate for a linear motor includes a metal plate and a plurality of permanent magnets arranged on the plate, and is used with an armature including windings. The permanent magnet provided on a surface of the magnet plate may be moved from a predetermined position upon large impact applied thereto. In order to prevent it, a linear motor including a magnet plate for positioning permanent magnets in position with the aid of an additional member protruding from the surface of the plate is known (see JP-B-2564851, JP-A-9-511380 and JP-A-2010-120055).
FIG. 12 is a sectional view illustrating an exemplary magnet plate 100 according to a known art. The magnet plate 100 includes a base plate 104, a plurality of permanent magnets 106, and a resin layer 108 formed on the base plate 104 and a surface of the permanent magnets 106. The base plate 104 has a plurality of protrusions 102 spaced apart from each other on a surface of the base plate 104. The permanent magnets 106 are situated between these protrusions 102. The protrusions 102 are intended to prevent the permanent magnets 106 from being misaligned in a transverse direction (a direction perpendicular to a longitudinal direction of the permanent magnet 106). FIG. 13 is a perspective view illustrating a process for forming the protrusions 102 on the magnet plate 100 shown in FIG. 12. In FIG. 13, only part of the base plate 104 and a cutting tool 110 are shown for simplicity. As illustrated, grooves 112 having a certain width are formed on the surface 104a of the base plate 104 by means of the cutting tool 110. Each of the protrusions 102 is formed between the adjacent grooves 112 to define side surfaces of the grooves 112.
FIG. 14 is a sectional view illustrating an exemplary magnet plate 120 according to another known art. FIG. 14 shows an armature 122 provided opposite to the magnet plate 120. A plurality of through holes 126 are formed in a base plate 124 of the magnet plate 120. Pins 128 are press-fitted to the through holes 126 so that parts of the pins 128 protrude from a surface 124a of the base plate 124. The pins 128 of the magnet plate 120 prevent misalignment of permanent magnets 130, similarly to the protrusions 102 described above with reference to FIG. 12. However, when a linear motor is used as driving means for driving a machine tool, liquid such as cutting fluid may enter the through holes 126 from a back surface 124b of the base plate 124, as illustrated by arrows. As a result, the pin 128 moves toward the armature 122 from a predetermined position, and there may be a risk of bringing a resin layer 132 into contact with the armature 122.
In the known art described in relation to FIGS. 12 and 13, a cutting process for forming protrusions tends to increase production cost. In the known art described in relation to FIG. 14, structural strength of protruding members attached to the base plate is not necessarily reliable. Accordingly, there is a need for an inexpensive magnet plate for a linear motor for preventing misalignment of magnets.